iOS 持久化存储策略

iOS persistent storage strategy(iOS 持久化存储策略)

问题描述

我正在开发一个将数据保存到本地文件系统的应用程序.将要保存的数据主要是 NSString 和 NSDate.数据不会经常保存，在典型使用情况下可能会输入 10 次新数据.数据当然也应该是可检索的(CRUD)

I'm developing an app which will save data to the local file system. The data that will be saved will be mostly NSString and NSDate. The data will not be saved that often, perhaps new data will be entered 10 times at a typical usage. The data should also of course be retrievable (CRUD)

我应该如何保存这些数据?首先是否有必要对这些对象进行建模?如果不是，我应该使用属性列表吗?还是 SQLLite3?

How should I save this data? First of all is it necessary to model these objects? If not should I use property lists? Or SQLLite3?

我是否应该归档课程模型?使用 SQLLite3?

Else should I archive the class models? Use SQLLite3?

我不小心遗漏了有关该应用程序的一些重要信息.实际上，我的应用程序将有 2 个具有聚合关系的数据模型.所以我的第一个数据模型(我们称之为 DataA)将有一个 NSString 和 NSDate 也将引用第二个数据模型(我们称之为 DataB)，它本身将由一个 NSString 和一个 NSArray 组成.所以现在变得有点复杂了.如果 DataB 中的一个对象被删除，它当然应该不再存在于 DataA 中(但 DataA 的其余部分应该保持不变)

I accidentally left out some vital information about the app. Actually my app will be having 2 data models which have an aggregated relationship. So my first data model (lets call it DataA) which will have a NSString and NSDate will also have a reference to the second data model (lets call it DataB) which itself will consist of a NSString and a NSArray. So it gets a little more complicated now. If an object from DataB gets deleted it should of course cease to exist in DataA (but the rest of DataA should be left untouched)

推荐答案

这种数据看起来很容易存储和检索，并且没有任何其他依赖，比如极其复杂的对象图.

This kind of data seems to be very simple to store and retrieve and does not have any other dependencies such as a horridly complex object graph.

您应该将此数据存储在平面文件或 NSUserDefaults 中.

You should store this data in a flat file or in NSUserDefaults.

我会给你一个例子，使用对象归档和 NSCoding 协议:

I'll give you an example of both, using object archiving with the use of the NSCoding protocol:

@interface ApplicationData <NSCopying, NSCoding> {}

@property (nonatomic, strong) NSDate *someDate;
@property (nonatomic, strong) NSDate *someOtherDate;

@property (nonatomic, copy) NSString *someString;
@property (nonatomic, copy) NSString *someOtherString;

@end

@implementation ApplicationData

@synthesize someDate = _someDate, someOtherDate = _someOtherDate, someString = _someString, someOtherString = _someOtherString;

- (NSArray *)keys {
   static dispatch_once_t once;
   static NSArray *keys = nil;
   dispatch_once(&once, ^{
      keys = [NSArray arrayWithObjects:@"someString", @"someOtherString", @"someDate", @"someOtherDate", nil];
  });
   return keys;
}

- (id) copyWithZone:(NSZone *) zone {
    ApplicationData *data = [[[self class] allocWithZone:zone] init];
    if(data) {
        data.someString = _someString;
        data.someOtherString = _someOtherString;     

        data.someDate = _someDate;
        data.someOtherDate = _someOtherDate;
        //...
    }
    return data;
 }

 - (void) encodeWithCoder:(NSCoder *) coder {
     [super encodeWithCoder:coder];

     NSDictionary *pairs = [self dictionaryWithValuesForKeys:[self keys]];

     for(NSString *key in keys) {
        [coder encodeObject:[pairs objectForKey:key] forKey:key];
     }
  }


  - (id) initWithCoder:(NSCoder *) decoder {
     self = [super initWithCoder:decoder];
     if(self) {
        for(NSString *key in [self keys]) {
           [self setValue:[decoder decodeObjectForKey:key] forKey:key];
        }
     }
     return self;
  }

  @end

然后，在您的应用程序委托中说，您可以这样做:

Then, say in your application delegate, you can do this:

@interface AppDelegate (Persistence)

@property (nonatomic, strong) ApplicationData *data;

- (void)saveApplicationDataToFlatFile;
- (void)loadApplicationDataFromFlatFile;
- (void)saveApplicationDataToUserDefaults;
- (void)loadApplicationDataFromUserDefaults;

@end

@implementation AppDelegate (Persistence) 
@synthesize data;

- (NSString *)_dataFilePath {
   static NSString *path = nil;
   static dispatch_once_t once;
   dispatch_once(&once, ^{
     path = [NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) stringByAppendingPathComponent:@"xAppData.dat"];
   });
   return path;
}

- (void)loadApplicationDataFromUserDefaults {        
   NSData *archivedData = [[NSUserDefaults standardUserDefaults] objectForKey:@"appData"];
   self.data = [NSKeyedUnarchiver unarchiveObjectWithData:archivedData];
}

- (void)saveApplicationDataToUserDefaults {
   NSData *archivedData = [NSKeyedArchiver archivedDataWithRootObject:self.data];
   [[NSUserDefaults standardUserDefaults] setObject:archivedData forKey:@"appData"];
   [[NSUserDefaults standardUserDefaults] synchronize];
}

- (void)loadApplicationDataFromFlatFile {
   NSData *archivedData = [NSData dataWithContentsOfFile:[self _dataFilePath]];
   self.data = [NSKeyedUnarchiver unarchiveObjectWithData:archivedData];
}

- (void)saveApplicationDataToFlatFile {  
   NSData *archivedData = [NSKeyedArchiver archivedDataWithRootObject:self.data];
   [archivedData writeToFile:[self _dataFilePath] atomically:YES];
}

@end

免责声明:我没有测试过这段代码.

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